An example of a patch formed by partially adhering a metal to a resin base material is a demetallized OVD. The recent mainstream of OVD forgery uses a metallization technique. Hence, a demetallized OVD is used to apply, to an OVD, a complex outline or minute pattern which is difficult to apply by metallization. For this reason, the demetallized OVD is employed in security products such as banknotes as a visual authenticity discrimination technique.
There are also many security products having a metal foil other than an OVD. In this case as well, the demetallization technique of partially adhering a metal to a resin base material to form a structure is used in the security products.
However, to accurately discriminate the authenticity of a security product such as a banknote, it is necessary to mechanically discriminate the authenticity of a patch such as a demetallized OVD formed by partially adhering a metal to a resin base material. Conventionally, to mechanically discriminate the authenticity of a patch, for example, a hologram having information embedded has been proposed (see, e.g., non-patent reference 1 to be described later). This technique directly forms a submicron structure on a metal surface by using a laser, thereby imparting unique information. This technique is used to identify a product sales route as a measure against, e.g., counterfeit name-brand products.
To inspect a printed product having a diffraction grating or hologram foil, a technique has been disclosed in which, for example, a metal coating is formed on the base material of a security thread by, e.g., vacuum deposition, chemical etching, or laser etching and partially removed in a repetitive pattern. A paper sheet having the security thread is passed through, e.g., a microwave detector, and the repetitive pattern of the security thread is compared with the pattern of an authentic printed product, thereby discriminating the authenticity (e.g., patent reference 1).
Security threads in the past are used to only detect whether a security thread is present, or whether a text is present on a security thread, i.e., the security thread is partially removed. However, the above-described technique takes a step forward and places focus on a fact that a security thread whose metal coating is partially removed in a repetitive pattern generates a predetermined microwave detected voltage waveform pattern. The microwave detected voltage waveform pattern is compared with that of an authentic printed product, thereby discriminating the authenticity.
There is also provided a security thread having a magnetic layer and a conductive layer on a base material, in which the conductive layer includes a conductive portion with a relatively high microwave detected voltage, and the conductive portion with the relatively high microwave detected voltage and magnetic data recorded in the magnetic layer are arranged in a predetermined positional relationship, thereby preventing any magnetic data reading error caused by a relative shift between the security thread and the printed product (e.g., patent reference 2).
This technique prevents any reading error of a machine regardless of a phase shift, allows not only the magnetic layer but also the conductive layer to carry transmittable data, and prevents any reading error in the forward and reverse directions.
There is also provided a metal deposited thermal transfer hologram sheet in which a metal deposition layer, or a metal layer and a thermal adhesive layer formed in advance are partially removed in a slit or mesh by laser machining, and a transparent or semitransparent pseudo hologram is formed in a region including the removed portion, and a method of processing the same (e.g., patent reference 3).
Non-patent reference 1: Proceedings of SPIE Vol. 4677 (2002), Direct Write method to create DOVIDs in metal surfaces
Patent reference 1: Japanese Patent No. 2906352 (Pages 1 to 5, FIGS. 1 to 4)
Patent reference 2: Japanese Patent Laid-Open No. 2002-348799 (Page 1, FIG. 1)
Patent reference 3: Japanese Patent Laid-Open No. 2003-226085